1. Field of Invention
This invention relates to systems and methods for thermal isolation of a silicon structure. In particular, the systems and methods of this invention relate to micromachined or microelectromechanical system based devices and the fabrication thereof.
2. Description of Related Art
It is know to thermally isolate a silicon structure from a substrate that supports the silicon structure. For example, an integrated optical circuit, as shown in FIG. 1, is described in international patent document WO 99/21036, published Apr. 29, 1999, which is incorporated herein by reference in its entirety. The device comprises a silicon on insulator (SOI) wafer including a layer of silicon 4 separated from a silicon substrate 5 by an insulator layer 6 formed of silicon dioxide. A portion of the layer of silicon 4 comprises a waveguide 1 that extends across a V-groove 2 formed in the silicon substrate 5. In that manner, the waveguide 1 is substantially thermally isolated from the silicon substrate 5.
As described in WO 99/21036, the waveguide 1 is a rib waveguide. An oxide coating 6A is formed over the rib waveguide 1 and an oxide layer 6 is formed under the rib waveguide 1. Temperature control means 9, such as metal coatings, are applied over the rib waveguide 1. By passing an electrical current therethrough, the temperature control means 9 are heated to heat the rib waveguide 1 and adjust the refractive index of the silicon of the rib waveguide 1. Because the rib waveguide 1 is substantially thermally isolated from the silicon substrate 5, the power and time required to heat the rib waveguide 1 are reduced.
The systems and methods of this invention provide thermal isolation of a silicon structure.
The systems and methods of this invention separately provide stress reduction for a silicon structure.
The systems and methods of this invention separately provide a substantially stress-free silicon structure.
The systems and methods of this invention separately provide a micromachined or microelectromechanical system based device with improved performance.
The systems and methods of this invention separately provide a micromachined or microelectromechanical system based device including a silicon structure that is at least partially thermally isolated from a substrate.
The systems and methods of this invention separately provide a micromachined or microelectromechanical system based device with improved manufacturability and reduced manufacturing costs.
The systems and methods of this invention separately provide thermal isolation of a silicon switch.
The systems and methods of this invention separately provide thermal isolation of a silicon waveguide.
According to various exemplary embodiments of the systems and methods of this invention, a micromachined device comprises a substrate, an insulation layer formed over at least part of the substrate, and a silicon layer formed over at least part of the insulation layer. The silicon layer includes a silicon structure that is at least partially thermally isolated from the substrate by a gap in the insulation layer and a surface of the substrate under the gap in the insulation layer is substantially unetched.
In various embodiments, the substrate is made of silicon. In various embodiments, the silicon layer is a single crystal silicon layer. In various embodiments, the insulation layer is made of silicon dioxide.
In various embodiments, the silicon structure is a thermo-optical switch. In various embodiments, the thermo-optical switch is a Mach-Zehnder switch.
According to various exemplary embodiments of the systems and methods of this invention, a micromachined device is fabricated by forming a substrate, forming an insulation layer over at least part of the substrate, forming a silicon layer over at least part of the insulation layer, forming a silicon structure in the silicon layer, and forming a gap in the insulation layer that at least partially thermally isolates the silicon structure from the substrate, wherein a surface of the substrate under the gap in the insulation layer is maintained substantially unetched.
According to other various exemplary embodiments of the systems and methods of this invention, a micromachined device is fabricated by forming a substrate, forming an insulation layer over at least part of the substrate, forming a silicon layer over at least part of the insulation layer, forming a silicon structure in the silicon layer, and forming a gap in the insulation layer without affecting a surface of the substrate underlying the gap.
In various embodiments, forming the gap in the insulation layer comprises removing a portion of the insulation layer with an etch that does not affect the substrate. In various embodiments, forming the substrate comprises forming a silicon substrate and removing the portion of the insulation layer is with an etch that does not affect silicon.
In various embodiments, forming the substrate comprises forming a substrate of a first material, forming the insulation layer comprises forming a layer of a second material, and forming the gap in the insulation layer comprises removing a portion of the insulation layer with an etch that is highly selective between the first and second materials.
In other various embodiments, forming the substrate comprises forming a substrate of silicon, forming the insulation layer comprises forming a layer of a dielectric material, and forming the gap in the insulation layer comprises removing a portion of the insulation layer with an etch that is highly selective between the dielectric material and silicon.
In other various embodiments, forming the substrate comprises forming a substrate of silicon, forming the insulation layer comprises forming a layer of silicon dioxide, and forming the gap in the insulation layer comprises removing a portion of the insulation layer with an etch that is highly selective between silicon dioxide and silicon.
These and other features and advantages of this invention are described in, or are apparent from, the following detailed description of various exemplary embodiments of the systems and methods according to this invention.